Target structure for color television display tubes



Oct. 29, 1957 E. M. MCMILLAN TARGET STRUCTURE FOR COLOR TELEVISION DISPLAY TUBES Filed Oct. 18, 1954 2 SheetsSheet l INVENTOR. fax/w M WWW/Amy Oct. 29, 1957 E. M. M MILLAN 2,811,661

TARGET STRUCTURE FOR COLOR TELEVISION DISPLAY TUBES Filed OCT. 18, 1954 I 2 Sheets-Sheet 2 73 z; 21 2 E? l 3.5 f? 3 1/ w l g L i I? f I; 29 1;

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INVENTOR. fiW/MMMM/AMM Uniwd W6 Patent 'HARGET STRUCTURE FUR COEOR T EI EEVISION vDISPLAIYTUBES EdwimMrM'cMillan,'Berkeley, cane, assignor to Chroma'tic Television Laboratories, "Inc., New York, N. Y., acorporation of California Application October 18, 1954, Serial No.462;69-8

10 'Claims. ;'(Cl. 313- 78) This invention relates to target structures for use in cathode-ray tubes for the display of television images in color, .which utilize post-deflection focusing to concenltrate an electron beam on a phosphor whichis emissive of a single color. Particularly it relates to .structures wherein the electronlenses utilized to focus the beam are the analogsof cylindrical optical lenses, and comprise a single .grid of closely spaced, parallel, linear conductors, tightly stretched and mounted adjacent to the display screen, in combination with a conducting coating on the surface of .the screen. In tubes of this character a plurality of ditterentphosphors are employed, respectively emissive of different colored light, on impact by the electron stream, the colors being components which additively produce White. The phosphors are disposed in strips extending across the surface of the display screen, generally parallel to the direction of the electrodes of the lens-grid. In a tricolor system, which is the most generally useful, the component colors emitted by the phospors will ordiinarily'be red, green, and blue, and a group of strips, in-

cluding at least oneof each of the three phosphors used, isie'le'ctro-optical1y centered behind the interspace between each pair of conductors of the grid, the other two phosphors being similarly centered behind the grid conductors.

Because of the fact that, in order to accomplish the focusing, the electrons constituting the beam are accelerated during their passage between grid and screen, their paths in this region are curved toward the axis'of the "tube and'the phosphor groups are therefore not geometrically alined with the center of deflection of thebeam as it'sc'ans "the screen surface. The amount of deviation of'the beam from its rectilinear course increases with its scanning deflection, and this deviation does not increase linearly with either the angle of scanning deflection or 'its'tangent, the latter being proportional to the distance from the center of the grid to the point'of penetration thereof by the electron beam.

The factors entering into the problem of .electro-optical alinement of the phosphor areas on the screen isdiscussed fully in the prior art. It is there shown that there are three related .quantities which affect the operation of a color televisiontube of this type. vFirst and most .important is the refraction of thebeam in its passage between grid and screen. If this is not correctly compensated for in the layout ofthe screen, thebeam-m-ay impact not only the wrong phosphor but actually the wrong groupof phosphors, rendering the tube inoperative forits intended purpose as color fidelity thus becomes impossible of achievement. The second factor which varies with-angle :of deflection is the degree through which the beam is concentrated or focusedrby the-electron lens system. The thirdfactonwhich is important only in tubes wherein the :color displayed is-controlled by micro-deflection of the fbeamn'at' the grid 'itself, is Fthe sensitivity 'to :such "de- :fiection. v rln tubes awherein micro-deflection is ward the ilin'ear wire.

2 conductors of the lens-grid are divided into .two interleaved groups, electrically insulated, so thatwhen elec- .trical potentials are applied betweenthe conductors of the two groups the beam is deflected toward the more positive electrode and directed to a phosphor :whichis electro-optically-alined with the more positive of the-two electrodes. The present invention attains its greatest value in tubes of the micro-deflection type, although it is not necessarily limited thereto.

It'has also previously been shown that by using a. more complicated-electron lens structure, employing a second grid, and specially shaped screens, all three of the quantities of refraction, focus, and deflection sensitivity may be compensated or made uniform over the entire surface of the screen. It is desirable, however, from the point of view of economy of construction and general utility, to utilize tubes wherein the envelope and screen conformationare more nearly like those employed in the tubes used for the display of monochrome images. Theoretically it is impossible to providecomplete'compensation ofall three of these quantities in'a tube employing two-elementelectron lenses at'the lens-grid. The broad purpose of thepresent invention, however, is to provide a target structure utilizing two-element electron lenses, in which the variations in the electro-optical parameters which affect the performance of a tube of this character are minimized, so that'the tube may be operated throughout substantially its full theoretical duty cycle, giving full brilliancy and high operative effectiveness, without employing additional and expensive compensating means to overcome the aberrations of the system. Other objects of the invention are to provide a structure Wherein the highly eflicient type of color-control grid utilizing tautly stretched wires can be used; to provide a type of target structure wherein the display screen may be deposited directly upon the tube face or window; to provide a device whose construction requires no complex mechanical features and wherein the grid structure can be constructed and positioned in the same general fashion as in the case .of planar grids and screens, utilizing 'only relatively slight modifications; and to provide a type of display tube which has advantages'both Yin lightness, economy of manufacture, and ease of construction over tubes heretofore used.

Broadly considered'the target structure of the present invention comprises the combination, in a cathode-ray tube which is otherwise of substantially conventional construction, of a lens grid of substantially circular,

cylindrical contour, concave as viewed from the electron gun, with a display screen deposited on a surface which is preferably also concave. The lens-grid is composed of tautly stretched, linear conductors, preferably fine The wires are parallel, substantially uniformly spaced, and form elements of the cylindrical surface dcfined by the grid, their spacing being of the order of magnitude of one elemental area of the television image to be reproduced by the tube. The display screen comprises strips of a'pluralityofdiiferent phosphors, preferably three, which are emissive, upon electron impact, of light of three component colors which additively pro duce white. The phosphor strips are disposed in groups or colorcells, each of which comprises all of the .phosphors, one such cell being electro-optically alined with each interspace between an adjacent pairof wires. As. will be shown hereinafter, by proper choice of the radii -of curvature of the grid and the screen, it is possible to In the drawings, illustrative of the detailed descriptions of certain embodiments of the invention which follow:

Fig. l is a semi-schematic, axial sectional view in plan of a television display tube embodying the invention, the plane of section being normal to the axis of the cylindrical grid structure;

Fig. 2 is a sectional view through the front end of the tube of Fig. l, the plane of section being parallei to the axis of the grid;

Fig. 3 is an isometric diagram of one form of frame for supporting a cylindrical grid structure;

Fig. 4 is a fragmentary elevational view of the grid structure, the direction of view being parallel to the cylinder axis.

Fig. 5 is a fragmentary cross-section of the grid structure, taken on the plane 55 of Fig. 4, illustrating the means of supporting and connecting to the grid conductors.

Fig. 6 is a fragmentary elevation of the target structure, showing the relationship between the grid conductors and the phosphor pattern at the center of the screen; and

Fig. 7 is a fragmentary cross-sectional view through the target, further showing the relationship between the grid conductors and the phosphor pattern.

Fig. 1 illustrates, diagrammatically, and in exaggerated form, a cathode-ray display tube embodying the present invention. Generally speaking, the tube is conventional in construction with the exception of the grid and screen structure, and it comprises evacuated envelope 1, having a generally funnel-shaped body, and an electron gun 3 mounted in the neck of the funnel. The electron gun may be of any conventional type, embodying a cathode, a control grid, and one or more anodes, adapted to direct a concentrated beam of electrons axially toward the larger end of the envelope. As the gun is conventional it is believed unnecessary to describe it in detail, since any of the many forms which have been devised for the purpose may be used. A base 5 includes plug connections for the various electrodes within the electron gun. In operation the beam is deflected from its axial path about a center of deflection or virtual source 7, to scan the target which forms the novel feature of the present invention. The deflection of the beam may be accomplished by a deflecting yoke mounted to encircle the neck of the tube or it may be accomplished by pairs of deflecting plates within the tube; these equivalents being well understood and the means for accomplishing the deflection not being a part of the present invention are not here shown.

A face plate or window 9 forms the larger end of the envelope. The body of the envelope 1 may be either of metal or of glass. In either case, in tubes of the character here described, the face plate or window 9 is made separately and is connected to the body of the tube at a seal 11 which encircles the envelope. Included in the seal or supported thereby is a ring 12 to which the grid structure next to be described is secured.

In the particular tube illustrated the grid comprises a rigid frame across which are strung two interleaved sets of tightly stretched linear conductors, in practice, most conveniently fine wires. The frame in this case comprises a pairof angles, 13, of structurally strong material. One web 13' at each end of each angle is bent at right angles, to form an abutment against which an insulating endbeam rests, supported by the unbent web, as illustrated in Figs. 3 and 4. The end-beam 15 may be formed of glass or ceramic. It is rectangular in cross-section, one face, that which rests against the webs of the angles 13, is preferably straight, while the other edge, to the right as illustrated in Fig. 4, is a substantially circular arc. This surface is provided with notches 14 at substantially uniform intervals, these notches serving to position the grid Wires. The end beams 15 are secured to the angle members 13 by bolts 16, which may also be used to attach the grid to the support ring 12. In the drawing the notches and wires are indicated symbolically, only a few being shown; in an actual tube the grid will comprise 500 or more conductors.

The linear conductors which form the grid are positioned by hooks in a manner best illustrated in Figs. 4 and 5. Two sets of these hooks are used on each of the beams 15. The hooks depend at right angles from continuous strips. One of these strips 17, from which the hooks 17 depend, is clamped between the web 13' and the beam 15, with the hooks extending under the lefthand surface of the beam as illustrated in Fig. 5. The continuous strip 19 of the other set lies at the left of the beam, with the hooks extending above it, as shown in this same figure.

The strips 17 and 19 are preferably secured to the beam with insulating cement which reinforces the clamping of the beam to the metal angles 13 insofar as the strip 17 is concerned, and holds the strip 19 in place for winding. A strip of insulation 21 overlies the continuous portion of the strip 19, and may also be temporarily cemented in place. The continuous conductor, in this case a fine wire 23, is then laced around the structure, engaging the hook 17'. The wires are tautly stretched and serve as an additional anchor for the strips 21 and hook strips 19, and the wires being positioned by alternate notches 14. The wires forming a conductor of the second set of grid wires are then laced in place, engaging the hooks 19', these wires passing over the wires of the first set without contact. It may be desirable to interpose additional insulation at the cross-over, or the insulation between the two sets may be accomplished merely by their spacing.

This particular structure is shown merely for completeness. Other arrangements can be used which give to the grid as a whole a cylindrical contour. The general arrangement is illustrated in Fig. 4.

The relationship of this grid to the bi-directionally curved window 9 of the tube, which is spherical in the case shown, is best illustrated in Figs. 1 and 2. It will be evident upon inspection the grid, in the plane of Fig. l, nearly uniformly spaced from the window upon which the fluorescent screen is deposited. In other planes this condition does not hold; it will be seen in Fig. 2 the screen approaches much more closely to the grid at the portions adjacent to the ends of the grid conductors. As will be shown hereinafter this precise arrangement is not a necessary condition for the invention, and the effects of various degrees of curvature of both grids and screen will be discussed in detail.

The screen used with this particular arrangement is of a type which is now well known. It comprises narrow strips of different phosphors which are emissive, upon electron impact, of light of three component colors which additively produce white. The phosphors are laid down in a repeating pattern, with the phosphor emissive of one color, preferably green, electro-optically centered between each pair of grid wires, as viewed from the center of deflection 7. A strip of phosphor emissive of one of the other colors, say red, is electro-optically centered behind each of the wires 23, with a strip emissive of the third color, say blue, centered elecro-optically behind each of the wires 25. Each pair of wires constitutes an aperture of a cylindrical electron lens. The width of the strips is such that the spacing on centers of the green strips (if the order of the strips is that here described) is equal to or less than the width of one elementary area which is to be resolved in the television image to be displayed upon the tube.

The phosphor pattern, as laid out in the manner thus described and illustrated fragmentarily in Figs. 6 and 7, is deposited upon the inner surface of the window 9 as indicated by the reference character 27. Overlying the phosphor coating is a film of conducting material, preferably aluminum, permeable to the cathode-ray beam which traces the television images presented. The dimensions of the phosphor layer and the conducting film which covers'it aretoo small -to be shownin the sectional views of Figs. 1 and 2; the fragmentaryviews' of Figsi6 and' 7, Fig. 6 illustrating the relationship of the phosphor strips to the. grid electrode at thecenter of the screen where the electro-optical alinement and the geometrical alinement coincide, and the cross-sectional view ofFig. 7, are greatly exaggerated for illustrative purposes. As willbe se'en in these figures there are two green strips'29 foreach re'd strip 31 and blue strip 33.

In Fig. 7 there is shown the conducting film'35, overlying the phosphor coating.

As has been stated, the fragmentary view of Fig. 7 illustrates the position, relatively, of the grid electrodes and'the phosphor strips at the screen center, where geometrical,-optical, electron-optical:positions coincide. In operation the grid wires are maintained at .a potential whichis positive to the cathode of the electron gun',while ,the fi lm35is positive tothe electrodes of the grid. Supertween any pair of grid wires. The amount that'the' beam is deflectedfrom its straight-line course'bytitsfocussing action depends both upon the relative potentials of the cathode, "grid, and screen, and its angle and direction of deflection about the center of deflectionindicatedby the point'7in Fig; 1. v s

It has previously been shown that'the three fundamental quali'tieswhich aflect the operation of the tube, i. e., re-

fr ction, deflection sensitivity, and width of focus, may befdefinedbyithe following equations:

7 I Refractioni' In terms of displacement from perpendicular from center of aperture: a

" v 12am 5;}, p I 13 1+\/1+.v;/ V1 osw) In 'ftcrms'ofldifierence' of displacement from straight lin pjath' o'f the rays between grid and screen: 1 7

. 2 v V 1+t T+'v' T/tvTcow' (1a.) Deflection sensitivity:

y vi-D'Vgi cosFfl/cos r] p l5l-1+ /1.+Vg/(V c03 t t.=D tan I n man a; 1 v ows/(mow) Fecal"width:' s g 1 r f .V [f cos B/cos ll! VI 1+ 1\ V V cos m in 1+ 1+V2/ V1 s w) v a 1 The notation used in these equations, and those which will f0ll0W,'iS as follows:- I D length of normal dropped from grid aperture pierced by 'bear'rrtoscreen 7 3 grid wire pitch wa er wire diameter Vi voltagebetween cathode and grid Vz=voltage between grid anarscreenx I .i =total angle between beam ='arriviiig at grid plane 'aiid normal dropped 'from "grid aperture pierced'byf beam pzzprojection of ,0 on plane normal to grid wires a=projection of #1 on plane parallelito grid wires which contains the normal'to the grid aperture pierced by the beam r=distance from beam impactpo'sitiomat screen to normal dropped from grid aperture pierced by beam y=projection of r on plane normal to grid wires t=refraction=deflection v of beam from. rectilinear paths between grid and screen These equations holdwherethe grid and: screen are "in parallel planes, and-they, are sufficiently accurate-for practical purposes with screen and grid curvatures such a's are met-with in tubessuch' as :areconsidered here if it be-as sumed that for any small-area impaeted by the beam-the grid is a plane tangent to its'actual surface and the screen lies in a parallel plane at adistance 'D-equal to the actual distance between the structures measured along-a perpendicular dropped from the grid. For planar grids and screens the quantity'D is a constant throughout the target area and the angleof incidence it is substantially the angle of scanning deflection; With curvedgridsandscreensthe quantity D' may become a variable, andthe-angle'wis-=in general less than the angle of deflection;

The problems in tube construction arise fromthe fact that all three of the'important quantities vary continuously, and nonlinearly with'both the angle of incidence 1,0 and its tangent, and that theydonot vary. ,in'exactly the same manner. a

7 Each of the i above equations shows that the 1 quantity involvedvaries at anincreasing rate with increasing angle of incidence at the grid. EquationsZ and 3 also show that the variation in size of the focalspot and thesensitivity to deflection both vary most "rapidlyiori deflections parallel to the direction 'of the grid conductors; so"much so,' infact, that in the case of the planar-' grid andrscreen the amount of variation in these quantities is-nearly-twice as great if thegrid conductors? run'parallel to "thelonger; dimension of the-screen as is the case if they run -paralleltothe shorter dimension;

According-to the preferred form 'of-the -present invention, therefore, the-axis 'of the cylindrical grid is in 'a plane parallel to'theshorter'dimension of the screen.

Theradius of curvature of the grid is greater-thanthe distance from the center ofdeflection ot the cathode-ray beam to the grid, in order to avoidexcessive-curvature of theviewin'g surface, but even so; the angle of incidence 0 is greatly decreased, so that the variationiin the three important parameters is not-only reduced but becomes much 'more nearly linear. Finally; in orderto' compensate for the angular variation" in sensitivity to deflection, the screen, to0,-'is preferablymade concave as viewed from the source of the; electron beam, preferably with 'a difierent degree of curvature from that applied to'th'e grid, so that the grid-screen 'dista'nce' 'b'ecomes"less as the sensitivity' to deflection increase'sg an'd 1 the displacement? of the focal spot thus mayb'e heldnearlyconstantp lBest compensation is obtained 'Whenth'e radii'ofcurvature ditfer' in the two dimensions,xbeing-longer in the plane parallel to-theaxis ofthe grid? A ve'ry considerable degree of compensation ca'n'beobtained, however, by making the screen with aninfinite radiusof -curvature in the direction'of the'grid axis (i..e.,'a-cylindrical screen) or with a spherically curved screen, whichvit may be ad'- vis'able'to use forreasons of screenmanufacture;

In order to design target structures in accordanc'ewith these principles it is necessary toexpress the quantities the beam at the grid, and;.h, thedistance of: the point or In the above equations J=the distance between the center of deflection of the cathode-ray beam and the axis of the cylindrical grid and R =the radius of the grid.

The expression for the quantity D differs in form slightly as between cylindrical, spherical, and compound-curved screens. For a cylindrical screen:

D=VR,(K sin 5) +K cos 5R,, For a spherical screen:

D= (R,-h )K sin 5+1: cos 5-R (8) In both of these equations K=the distance the center of curvature of the screen is displaced toward the grid from the grid axis, and Rs is the radius of curvature of the screen at the point .of impact, in the plane of deflection of the beam.

With a tube of given externaldimensions one method of design, by the use of the above equations, is to determine first the parameters of the grid which is to be used, solve the equations for variation in focus and sensitivity, giving the latter in terms of the screen distance D, and finally, through the use of the equations, choose radii of curvature for the screen so that D will vary inversely as its coefiicient in the solutions.

The closest approximation to uniformity of deflection sensitivity can be achieved with a screen having a barrelshaped" surface; i. .e., a surface which is generated by rotating an arc of long radius around the axis on a shorter radius. r In this case the equations for a cylindrical screen maybe applied to obtain the values of the shorter radii in the planes passing through center and the edges of the screen. The longer radius of the screen is that of a circle passing through the ends of these radii.

This construction leads to screens which are very nearly cylindrical; in a tube having a maximum angle of deflection 0 of. 35, with a projected screen area of 10 /2 x 14 inches and a distance from the center of deflection to the screen of 13 inches, it leads to minor radii of approximately 27 inches and major radii in the neighborhood of 150 inches, with a difference between the lengths of the minor radii at the center and ends of the screen of somewhere in the neighborhood of bio inch. Using a grid wire spacing of 30 mils and a ratio Vz/ V1 of 2.76, the variation in spot size at the extremes of the X and Y axes is only about 1.8 mils. This is less than one-half of the minimum variation obtainable with a flat grid and the same angles of deflection. The variation in eiiective sensitivity to deflection, over the screen surface, is re ducedto one or two percent.

Using a cylindrical screen with the same type of grid, the variation in sensitivity 'to deflection becomes somewhat greater, butis still only about one-halfofthat ob tained with planar grids and screens.

Where the screen is formed directly on the window at the end of the tube, a screen cylindrical or nearly cylindrical in form is more difiicult to manufacture than that employing a spherical surface. For the purpose of economy of manufacture, it may therefore be desirable to use a compromise design wherein the sensitivity to deflection is perr'nittedto vary but the variation in focus is held to a minimum. A tube having a spherical-surface screen, with a 40 inch radius and with a center of curvature of the screen on theaxis onthe. cylindrical grid and wit-h one '8 inch maximum separation between grid and screen will have the following characteristics:

Point Refraction Deflection Focusing Correction Center of Screen 0 1 06 Center of Vertical Edge"-.. 10 1.025 04 Center of Horizontal Edge 0 0.71 0. 06 Corner of Screen 0. 076 0.71 06 This is assuming a voltage ratio -ZZ-=Z.75.

Such a construction leads to a large improvement in variation in focal-spot size as compared to a flat grid and screen. The variation in deflection sensitivity is substantially the same as in the case of the planar grid and screen.

It should be evident that an infinite number of variations is possible between a cylindrical or nearly cylindrical screen surface and a spherical surface, thus offering a compromise between ease of manufacturing construction and uniform sensitivity to deflection. The use of the curved grid, however, always reduces the variation in spot size. This, of itself, leads to improved performance, since in order to prevent color contamination in the picture displayed it is desirable to blank the spot during the intervals when it is passing over the junction between two adjacent strips of phosphor. The faster the spot is traveling when it crosses the junction between two phosphors the larger it may be for a given blanking interval.

With such a cylindrical grid and spherical screen the maximum sensitivity to deflection occurs at the center of the screen, instead at the ends of the strips as is the case with planar structures. For this reason it may be desirable to choose the value of V2/ V1 so that minimum spot size is obtained nearer to the edges of the screen instead of equalizing the increase in size due to over-focusing at the edges and under-focusing at the center. By making the phosphor strip which is electro-optically centered with the centers of the corresponding apertures wider than the two adjacent strips, electro-optically centered under the electrodes, minimum blanking time may thus be obtained.

Experience has indicated that owing to the scattering of both electrons and light in the phosphor, and of aberrations of the electron-optical lenses, the minimum size of spot which can be obtained is approximately 3 mils in width. By adjusting the value of V2/ V1 so that the degree of over-focus at the edges is about one-third of the degree of under-focus at the center of the screen the transition time can be equalized and optimum performance obtained.

The advantages in regard to its variation in size in focal spot and variation in deflection sensitivity have been emphasized throughout this specification because it is always possible to devise a screen which will properly take account of refraction. Methods of closely approximating the exact corrections by dividing the target area into zones are described in the prior art. Nevertheless there is a definite advantage in the use of the cylindrical grid even so far as refraction is concerned, since, with the smaller eflective angles of incidence resulting from its use, the variation in refraction becomes much more nearly linear and if refraction is to be compensated for by any of the approximate methods, which divide the screen area into zones, the number of zones used can be reduced or, alternatively, the residual errors between zones may be minimized if the same number of zones are employed as for a flat grid.

It may be of interest to note the effect of other grid and screen conformations. By increasing the radii of curvature of either a cylinder or a sphere the result, in the limit, is a fiat screen. As has been pointed out, the use of a concavely cylindrical grid improves the overall focusing to the same degree,iirrespective of the curvature ofthescreen, since electron lenses of the type here described result in the same variation in size'of focal spotwith variation in the angle of incidence of the beam irrespective of the separation D between screen and grid If,'in the limiting case, the concavely cylindrical grid is used with a flat screen, the improvement'in focus will be the same as with a concave screen. The variation in sensitivity of deflection may be either greater or less than-with a flat grid, depending upon whetherithe percentage variation in D resulting from the greater distance between grid and screen at'the edges of the structure is greateror less, proportionally, than the variation in angular sensitivity; with relatively large minimum values of D there may; therefore, be improvement in performance even in the case of a fiat screen with the concave grid.

If a convex grid were used, the variation in effective angle of incidence would be greatly increased, the variation in focus would be increased, and although the variation in sensitivity might possibly be decreased at some particular value, in general the whole performance of the tube would be deteriorated.

In the case oftubes wherein'the color displayed depends uponthe angle of incidence of the beam at the grid and not upon micro-deflection, the problem of deflection sensitivity no longer appears as such but since the variation in angle of incidence has an eifect generally similar to micro-deflection with respect to the points of beam impact on various portions of-the screen the concave grid can still give improved results with proper "screen configuration.

So many diiferent parameters and manufacturing considerations are involved in the structure of a color tube that itis not, practical or even possible to define a best combinations of parameters. Diiferent engineers -will choose different combinations to meet specific conditions of manufacturing simplicity, ruggedness of structure, and uniformity of operation throughout the screen area. The various examples given herein are illustrative, therefore, rather than limiting conditions. These examples are therefore not intended to be considered as limiting the scope of the invention, the intended limitations being set forth specifically in the following claims.

What is claimed is as follows:

1. In a cathode-ray tube for the display of television images in color, comprising an evacuated envelope and an electron gun therein adapted to direct an electron beam against a viewing area at one end thereof over which the beam is adapted to be deflected about a center of deflection to scan said viewing area, a target structure within said viewing area comprising a transparent base having a substantially uniformly curved concave surface facing said electron gun, a grid of tightly stretched linear conductors mounted adjacent to said base, said conductors being disposed along elements of a cylindrical surface having its axis substantially parallel to an axis of symmetry of said concave surface and being mutually spaced by distances of the order of magnitude of one elemental area of the television image to be reproduced, and a display screen deposited on the concave surface of said base and comprising strips of different phosphors respectively emissive on electron impact of light of the component colors of an additive color system and disposed in a repeating pattern of groups, each of which includes at least one strip of each of said phosphors, the center of each group being electro-optically alined with the center of the interspace between an adjacent pair of electrodes of said grid.

2. In a cathode-ray tube for the display of television images in color, comprising an evacuated envelope and an electron gun therein adapted to direct an electron beam against a viewing area at one end thereof over which the beam is adapted to be deflected about a center of deflection to scan said viewing area, a target structure within said viewing area comprising atransparent base having a substantially spherically curved concave surface facing said electron gun, a grid oftightlystretchedlinearconductors mounted adjacent-to said base, said conductors being disposed along elements of a cylindrical surface having itsaxissubstantially parallel to'the chord of" said spherical surface and being mutually spaced by distances of the order of magnitude of one elemental area of the televisionimage to be reproduced, and a display screen deposited on the concave surface of said base and comprising strips of'different phosphors respectively emissive on electron impactof light of the component colors of an additive color system and disposed in a repeating'pattern of groups, each of which includes at least one'strip of each'of said phosphors, the center of each group being electro-optically alined with the center of the interspace between an adjacent pair of electrodes of said grid.

3. The combination as defined in claim 2 wherein the center of said spherical surface and the axis of the cylinder defined by said grid are each more distant from said target structure than the center of deflection" of said beam.

4. In a display tube for television signals including means fordirecting a beam of electrons in a direction substantially normal to a target area over which it is adapted to be deflected bidirectionally to scana raster, target structure Within said area comprising a grid of parallel linear. conductors disposed in two mutually insu lated, interleaved sets and defining a cylindrical surface, connections for applying potential differences between said setsto produce a micro-deflection of electrons passing therebetween, and a display screen mounted adjacent to said grid and comprising a transparent base, strips of phosphors emissive on electron impact of light of different colors additively producing white disposed on said base in a repeating pattern of groups including all of said phosphors, the centerof each group being electro-optically alined with the center of an interspace between adjacent conductors of said grid, and a conductive coating on said phosphors adapted to form with said grid elements of a multiplicity of electron lenses, the phosphorcoated surface of said base being concavely curved with respect to said grid in at least one dimension so that the separation between said grid and screen varies from pointto-point over the surface thereof as an inverse function of the angle of incidence of said beam at said grid when deflected thereto. a

5. In a display tube for television signals including means for directing a beam of electrons in a direction substantially normal to a target area over which it is adapted to be deflected bidirectionally to scan a raster, target structure within said area comprising a grid of parallel linear conductors disposed in two mutually insulated, interleaved sets and defining a cylindrical surface, connections for applying potential differences between said sets to produce a micro-deflection of electrons passing therebetween, and a display screen mounted adjacent to said grid and comprising a transparent base, strips of phosphors emissive on electron impact of light of different colors additively producing white disposed on said base in a repeating pattern of groups including all of said phosphors, the center of each group being electrooptically alined with the center of an interspace between adjacent conductors of said grid, and a conductive coating on said phosphors adapted to form with said grid elements of a multiplicity of electron lenses,.the phosphorcoated surface of said base being concavely curved with respect to said grid in at least one dimension so that the separation between said grid and screen varies from pointto-point over the surface thereof substantially in inverse proportion to the sensitivity to angular micro-deflection of said beam at said grid when deflected thereto as such sensitivity varies with the varying angles of incidence of said beam at said grid.

6. In a display tube for television signals including means for directing a beam of electrons in a direction substantially normal to a target area over which it is adapted 11 to be deflected bidirectionallyto scan a raster, target structure within said area comprising a grid of parallel linear conductors disposed in two mutually insulated, interleaved sets and defining a cylindrical surface, connectionsfor applying potential diiferences between said sets to produce a micro-deflection of electrons passing therebetween, and a display screen mounted adjacent to said grid and comprising a transparent base, strips of phosphors emissive on electron impact of light of different colors additively producing white disposed on said base in a repeating pattern of groups including all of said phosphors, the center of each group being electro-optically alined with the center of an interspace between adjacent conductors of said grid, and a conductive coating on said phosphors adapted to form with said grid elements of a multiplicity of electron lenses, the phosphor-coated surface of said base being concavely curved with respect to said grid with difierent degrees of curvature in the two dimensions, so that the separation between grid and screen varies from point-to-point with the variation in angle of incidence of said beam at said grid and varies more rapidly with angles of incidence parallel to the direction of the electrodes of said grid than with angles of incidence normal thereto.

7. In a cathode-ray tube for displaying television images in color which includes a screen having a repeating pattern of strips of phosphors emissive of different colored light deposited thereon and an electron gun for directing against said screen a beam of electrons adapted to be bidirectionally deflected thereacross about a center of deflection screen, a grid of tightly stretched linear conductors mounted adjacent to said screen, the conductors of said grid being disposed generally parallel to the phosphor strips comprising said pattern and defining a cylindrical surface having an axis more distant from said screen than said center of deflection, said surface being concave as viewed from said electron gun.

8. A grid as defined in claim 7 wherein the conductors of said grid comprise two mutually insulated interleaved sets. 1

9. In a cathode-ray tube for displaying television images in color, including an electron gun for directing a beam of cathode rays against a target area over which said beam is adapted to be bidirectionally deflected about a center of deflection to trace a raster, a grid of tightly stretched substantially parallel linear conductors disposed in a cylindrical surface mounted in said target area, said surface being concave toward said electron gun and having a radius of curvature greater than the distance of said center of deflection to said grid, and a screen mounted behind said grid in said target area and concave as viewed from said electron gun and comprising a transparent base plate and a repeating pattern of strips of different phosphors deposited thereon, said strips being generally parallel to said linear conductors, said screen being so curved as to be nearer to said grid at the ends of said linear conductors than at the centers thereof.

10. The combination as defined in claim 9 wherein the dimensions of said grid and screen are less in the direction of the axis of said grid than in the direction normal to said axis.

References Cited in the file of this patent UNITED STATES PATENTS Re. 23,672 Okolicsanyi June 23, 1953 2,566,713 Zworykin Sept. 4, 1951 2,606,303 Bratnley Aug. 5, 1952 2,635,203 Pakswer Apr. 14, 1953 2,692,532 Lawrence Oct. 26, 1954 2,696,571 1 Law Dec. 7, 1954 

